The present invention relates generally to permanent magnet motors, and more particularly, to an improved magnet polarity detection technique for position sensorless permanent magnet motors, such as those that are used in electric vehicle and other applications.
The assignee of the present invention designs and develops electric vehicles and permanent magnet motors that are used to propel such vehicles. By using a technique disclosed in U.S. Pat. No. 5,585,709 issued to Jansen, for example, one can detect the position of a rotor of the permanent magnet motor but not the magnetic polarity. That is, the absolute position of the rotor is either the detected angle or the detected angle plus 180 degrees. This is due to the fact that the change in motor inductance is periodic over 180 electrical degrees, not 360 as would be required for unique detection. The present invention provides a solution to this problem.
It would therefore be desirable to have an improved magnet polarity detection technique for position sensorless permanent magnet motors.